Wireless communication systems have become an important means by which many people worldwide have come to communicate. A wireless communication system interconnects many nodes by using electromagnetic waves, such as radio waves, rather than wires commonly used in a fixed telephone network system. A wireless communication system often consists of many mobile devices and a plurality of base stations. A base station serves a mobile device when the mobile device enters a region associated with the base station.
A modern communication system includes many interconnected networks, which consist of both wireless networks and fixed networks. In a modern communication network, each mobile device has its own internet protocol (IP) address. The IP addresses are used to transmit data packets from one mobile device to another device. In order to serve a mobile device while it is travelling (or roaming) from a registered network to a visited network, Mobile IP has been proposed by the Internet Engineering Task Force (IETF) to allow mobile device users to move from one network to another while maintaining a permanent IP address.
A version of Mobile IP is Mobile IP version 6 (MIPv6). In a MIPv6 based communication system, a mobile device has a home address (HoA). When the mobile device changes its location and moves into a visited network, it receives a care-of address (CoA) from the visited network. In a MIPv6 mobile network, the mobile device then sends a binding update to a home agent in its home network. The binding update causes the home agent to establish a binding between the HoA and the CoA. Subsequently, the home network forwards data packets destined to the mobile device's HoA to the mobile device's current CoA.
Proxy MIPv6 (PMIPv6) is a variant of MIPv6 where the mobile device is not involved in the updating of its current location. Instead, PMIPv6 relies on a proxy mobility agent, such as Mobile Access Gateway (MAG), to detect a mobile device's attachments and detachments and signal the binding update to the a local mobility anchor (LMA). PMIPv6 is promulgated to support an efficient binding update by assigning the proxy agents, such as the MAGs, to report the location change to the home LMA.
One disadvantage of the existing PMIPv6 based network is the triangle routing problem caused by having the LMA in one single network and illustrated in FIG. 1. FIG. 1 includes a home network 140, a home LMA (H-LMA) 150, a visited network 130, a MAG 160, a Mobile Node (MN) 110 and a Correspondent Node (CN) 120. The CN is a communication partner of the MN. The MN 110 and the CN 120 are geographically close to each other, but both the MN 110 and the CN 120 may be far away from the H-LMA 150. The MN 110 is located within a visited network 130.
In a PMIPv6 network, the MN 110 may be a notebook computer, a mobile phone or a PDA. The MN 110 has two IP addresses in a PMIPv6 network. The H-LMA 150 allocates an HoA to the MN 110. The HoA is used to communicate with the CN 120. This address does not change and serves the purpose of identification of the MN 110. In contrast, a CoA or proxy-CoA is a temporary address for an MN 110 to receive packets when it visits a foreign network. In this PMIPv6 network example, when the MN 110 moves from the H-LMA 150 and enters a visited network, the MAG 160 detects the attachment and signals a binding update to the H-LMA 150 located in the home network 140. The H-LMA 150 binds the CoA or proxy-CoA of the MAG 160 with the HoA to map the MN's 110 current routing location with its HoA.
When the CN 120 sends messages to the MN 110, the messages are addressed to the HoA of the MN 110. In accordance with the home address attached with the messages, the messages are directed to the home network where the H-LMA 150 intercepts the message. The H-LMA 150 tunnels the messages to the MN 110's visited network based on its CoA or the MAG 160 in the MN 110's visited network. The network repeats this triangle routing until all messages from the CN 120 reach the MN 110. Accordingly, the communication path is unnecessarily long, and results in inefficient routing and high message delays.
This triangle problem may be accentuated when a network utilizing the PMIPv6 network attempts to communicate to another, separate network systems or domains, such as a network which may be owned by another service provider. In such a case, the triangle problem may occur in both networks. That is, when the MN 260 belonging to one network system 200 served by one H-LMA 215 communicates with a second MN 295 belonging to another network 205 served by another H-LMA, the packet will traverse both the first H-LAM 215 and the second H-LMA 265, thereby causing a delay during each transmission of data.
Accordingly, what is needed in the art is an optimized mobility routing for a system having two separate networks.